// Copyright 2014 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/base/bits.h"

#include <limits>

#include "src/base/logging.h"

namespace v8 {
namespace base {
    namespace bits {

        uint32_t RoundUpToPowerOfTwo32(uint32_t value)
        {
            DCHECK_LE(value, uint32_t { 1 } << 31);
            if (value)
                --value;
// Use computation based on leading zeros if we have compiler support for that.
#if V8_HAS_BUILTIN_CLZ || V8_CC_MSVC
            return 1u << (32 - CountLeadingZeros(value));
#else
            value |= value >> 1;
            value |= value >> 2;
            value |= value >> 4;
            value |= value >> 8;
            value |= value >> 16;
            return value + 1;
#endif
        }

        uint64_t RoundUpToPowerOfTwo64(uint64_t value)
        {
            DCHECK_LE(value, uint64_t { 1 } << 63);
            if (value)
                --value;
// Use computation based on leading zeros if we have compiler support for that.
#if V8_HAS_BUILTIN_CLZ
            return uint64_t { 1 } << (64 - CountLeadingZeros(value));
#else
            value |= value >> 1;
            value |= value >> 2;
            value |= value >> 4;
            value |= value >> 8;
            value |= value >> 16;
            value |= value >> 32;
            return value + 1;
#endif
        }

        int32_t SignedMulHigh32(int32_t lhs, int32_t rhs)
        {
            int64_t const value = static_cast<int64_t>(lhs) * static_cast<int64_t>(rhs);
            return bit_cast<int32_t, uint32_t>(bit_cast<uint64_t>(value) >> 32u);
        }

        int32_t SignedMulHighAndAdd32(int32_t lhs, int32_t rhs, int32_t acc)
        {
            return bit_cast<int32_t>(bit_cast<uint32_t>(acc) + bit_cast<uint32_t>(SignedMulHigh32(lhs, rhs)));
        }

        int32_t SignedDiv32(int32_t lhs, int32_t rhs)
        {
            if (rhs == 0)
                return 0;
            if (rhs == -1)
                return lhs == std::numeric_limits<int32_t>::min() ? lhs : -lhs;
            return lhs / rhs;
        }

        int32_t SignedMod32(int32_t lhs, int32_t rhs)
        {
            if (rhs == 0 || rhs == -1)
                return 0;
            return lhs % rhs;
        }

        int64_t SignedSaturatedAdd64(int64_t lhs, int64_t rhs)
        {
            using limits = std::numeric_limits<int64_t>;
            // Underflow if {lhs + rhs < min}. In that case, return {min}.
            if (rhs < 0 && lhs < limits::min() - rhs)
                return limits::min();
            // Overflow if {lhs + rhs > max}. In that case, return {max}.
            if (rhs >= 0 && lhs > limits::max() - rhs)
                return limits::max();
            return lhs + rhs;
        }

        int64_t SignedSaturatedSub64(int64_t lhs, int64_t rhs)
        {
            using limits = std::numeric_limits<int64_t>;
            // Underflow if {lhs - rhs < min}. In that case, return {min}.
            if (rhs > 0 && lhs < limits::min() + rhs)
                return limits::min();
            // Overflow if {lhs - rhs > max}. In that case, return {max}.
            if (rhs <= 0 && lhs > limits::max() + rhs)
                return limits::max();
            return lhs - rhs;
        }

        bool SignedMulOverflow32(int32_t lhs, int32_t rhs, int32_t* val)
        {
            // Compute the result as {int64_t}, then check for overflow.
            int64_t result = int64_t { lhs } * int64_t { rhs };
            *val = static_cast<int32_t>(result);
            using limits = std::numeric_limits<int32_t>;
            return result < limits::min() || result > limits::max();
        }

    } // namespace bits
} // namespace base
} // namespace v8
